This invention relates to precision optical elements, such as optical lenses, having one or more optical surfaces, particularly one or more, aspheric optical surfaces. This invention quite particularly relates to lenses having one or more fiducial surfaces which can serve as references for precisely determining the location and/or the alignment of the lenses' aspheric surfaces relative to one another and relative to optical systems which contain the lenses. This invention more particularly relates to molded glass lenses having aspheric surfaces and fiducial surfaces in precise locations and alignments relative to one another.
The vast majority of lenses used today in optical systems have spherical optical surfaces. The point symmetry of the spherical surfaces of such lenses makes it possible to locate the optical axes of these surfaces by simple mechanical methods (e.g., by edging techniques) after the surfaces have been fabricated. The symmetry of the spherical surfaces of such lenses also makes it relatively simple to align such surfaces in an optical system. This is because the only misalignment of spherical surfaces that can occur is due to decentration which is relatively easy to correct.
Lenses with aspheric optical surfaces have significant optical advantages over lenses with spherical surfaces. For example, an aspheric lens can be designed so that it does not produce spherical aberration or coma in an optical system. However, the use of aspheric lenses has not been widespread. One reason has been the difficulty of fabricating such a lens with aspheric surfaces having precisely known locations and alignments. In this regard, it has been difficult to determine precisely the location and alignment of the axis of symmetry of an aspheric surface of such a lens during its fabrication, testing and/or end use.
Heretofore, the only way of precisely determining the location and alignment of an aspheric surface has involved measuring the exact contour of the aspheric surface (e.g., with a mechanical stylus or interferometrically). Such a measurement has been inherently complicated and time-consuming to carry out. Also, such a measurement has frequently been impossible (e.g., due to space limitations) to carry-out in certain optical systems. Alternative ways have been sought, therefore, for precisely determining the location and alignment of an aspheric surface of a lens.